| Don't scale images in the browser (avoidScalingImages) | The page has 1 image that are scaled more than 100 pixels. It would be better if those images are sent so the browser don't need to scale them. | 90 |
| Description: It's easy to scale images in the browser and make sure they look good in different devices, however that is bad for performance! Scaling images in the browser takes extra CPU time and will hurt performance on mobile. And the user will download extra kilobytes (sometimes megabytes) of data that could be avoided. Don't do that, make sure you create multiple version of the same image server-side and serve the appropriate one. |
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| Avoid slowing down the critical rendering path (fastRender) | The style https://teacher.skyeng.ru/assets/669a2253a96c97c3aad1ea34f0ae0a06.css is larger than the magic number TCP window size 14.5 kB. Make the file smaller and the page will render faster. Avoid loading synchronously JavaScript inside of head, you shouldn't need JavaScript to render your page! The page has 1 render blocking CSS request and 5 blocking JavaScript requests inside of head. | 45 |
| Description: The critical rendering path is what the browser needs to do to start rendering the page. Every file requested inside of the head element will postpone the rendering of the page, because the browser need to do the request. Avoid loading JavaScript synchronously inside of the head (you should not need JavaScript to render the page), request files from the same domain as the main document (to avoid DNS lookups) and inline CSS or use server push for really fast rendering and a short rendering path. |
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| Avoid using Google Tag Manager (googletagmanager) | The page is using Google Tag Manager, this is a performance risk since non-tech users can add JavaScript to your page. | 0 |
| Description: Google Tag Manager makes it possible for non tech users to add scripts to your page that will downgrade performance. |
| Inline CSS for faster first render (inlineCss) | The page has both inline CSS and CSS requests even though it uses a HTTP/2-ish connection. If you have many users on slow connections, it can be better to only inline the CSS. Run your own tests and check the waterfall graph to see what happens. | 95 |
| Description: In the early days of the Internet, inlining CSS was one of the ugliest things you can do. That has changed if you want your page to start rendering fast for your user. Always inline the critical CSS when you use HTTP/1 and HTTP/2 (avoid doing CSS requests that block rendering) and lazy load and cache the rest of the CSS. It is a little more complicated when using HTTP/2. Does your server support HTTP push? Then maybe that can help. Do you have a lot of users on a slow connection and are serving large chunks of HTML? Then it could be better to use the inline technique, becasue some servers always prioritize HTML content over CSS so the user needs to download the HTML first, before the CSS is downloaded. |
| Avoid CPU Long Tasks (longTasks) | The page has 32 CPU long tasks with the total of 3961 ms. However the CPU Long Task is depending on the computer/phones actual CPU speed, so you should measure this on the same type of the device that your user is using. Use Geckoprofiler for Firefox or Chromes tracelog to debug your Long Task. | 0 |
| Description: Long CPU tasks locks the thread. To the user this is commonly visible as a "locked up" page where the browser is unable to respond to user input; this is a major source of bad user experience on the web today. However the CPU Long Task is depending on the computer/phones actual CPU speed, so you should measure this on the same type of the device that your user is using. |
Offenders: - multiple-contexts
- self
- self
- self
- multiple-contexts
- self
- self
- self
- multiple-contexts
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- cross-origin-descendant
- multiple-contexts
- multiple-contexts
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| Avoid doing redirects (assetsRedirects) | The page has 4 redirects. 4 requests are from other domains, it could be 3rd-party assets doing unnecessary redirects. :( | 60 |
| Description: A redirect is one extra step for the user to download the asset. Avoid that if you want to be fast. Redirects are even more of a showstopper on mobile. |
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| Avoid extra requests by setting cache headers (cacheHeaders) | The page has 203 requests that are missing a cache time. Configure a cache time so the browser doesn't need to download them every time. It will save 2.8 MB the next access. | 0 |
| Description: The easiest way to make your page fast is to avoid doing requests to the server. Setting a cache header on your server response will tell the browser that it doesn't need to download the asset again during the configured cache time! Always try to set a cache time if the content doesn't change for every request. |
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| Long cache headers is good (cacheHeadersLong) | The page has 52 requests that have a shorter cache time than 30 days (but still a cache time). | 48 |
| Description: Setting a cache header is good. Setting a long cache header (at least 30 days) is even better beacause then it will stay long in the browser cache. But what do you do if that asset change? Rename it and the browser will pick up the new version. |
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| Total CSS size shouldn't be too big (cssSize) | The total CSS transfer size is 70.3 kB and uncompressed size is 2.1 MB. I don't know what to say, the page needs more than 2 MB CSS to render. | 50 |
| Description: Delivering a massive amount of CSS to the browser is not the best thing you can do, because it means more work for the browser when parsing the CSS against the HTML and that makes the rendering slower. Try to send only the CSS that is used on that page. And make sure to remove CSS rules when they aren't used anymore. |
| Avoid too many fonts (fewFonts) | The page has 9 font requests. Do you really need them? What value does the fonts give the user? | 10 |
| Description: How many fonts do you need on a page for the user to get the message? Fonts can slow down the rendering of content, try to avoid loading too many of them because worst case it can make the text invisible until they are loaded (FOIT—flash of invisible text), best case they will flicker the text content when they arrive. |
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| Total JavaScript size shouldn't be too big (javascriptSize) | The total JavaScript transfer size is 3.9 MB and the uncompressed size is 84.1 MB. This is totally crazy! There is really room for improvement here. | 0 |
| Description: A lot of JavaScript often means you are downloading more than you need. How complex is the page and what can the user do on the page? Do you use multiple JavaScript frameworks? |
| Avoid using incorrect mime types (mimeTypes) | The page has 12 misconfigured mime types. | 88 |
| Description: It's not a great idea to let browsers guess content types (content sniffing), in some cases it can actually be a security risk. |
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| Make each CSS response small (optimalCssSize) | https://teacher.skyeng.ru/assets/669a2253a96c97c3aad1ea34f0ae0a06.css size is 35.6 kB (35565) and that is bigger than the limit of 14.5 kB. https://teachers.skyeng.ru/styles.fdf9a3381f615554dc8b.css size is 33.7 kB (33712) and that is bigger than the limit of 14.5 kB. Try to make the CSS files fit into 14.5 KB. | 80 |
| Description: Make CSS responses small to fit into the magic number TCP window size of 14.5 KB. The browser can then download the CSS faster and that will make the page start rendering earlier. |
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| Total page size shouldn't be too big (pageSize) | The page total transfer size is 4.8 MB, which is more than the coach limit of 2 MB. That is really big and you need to make it smaller. | 0 |
| Description: Avoid having pages that have a transfer size over the wire of more than 2 MB (desktop) and 1 MB (mobile) because that is really big and will hurt performance and will make the page expensive for the user if she/he pays for the bandwidth. |
| Don't use private headers on static content (privateAssets) | The page has 97 requests with private headers. Make sure that the assets really should be private and only used by one user. Otherwise, make it cacheable for everyone. | 0 |
| Description: If you set private headers on content, that means that the content are specific for that user. Static content should be able to be cached and used by everyone. Avoid setting the cache header to private. |
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